Chevelle SS396 Dyno Test - Calling Dr. Dyno!

We Squeeze Some Extra Ponies Out Of A 396/325 '69 Chevelle With Some Chassis-Dyno Tuning

After a drag test of this Glacier Blue '69 Chevelle SS396, we decided a trip to the chassis dyno to eek some more power out of this bad boy was needed. The results may surprise you.

In this day and age, when money is tight and the economy forces us to tighten our belts, we're all about free horsepower. While the big stroker fat-block is cool, along with that honking 6-71 blower, if the money isn't there, then you have to go about adding power the old-fashioned way-through dyno tuning.

With that in mind, we tackled the task of trying to add as much power as we could to this dream machine, a '69 Chevelle SS packing the legendary 396 big-block. Not the 375-hp version, this car's near-stock 325-hp engine was in need of some power. The owner was thrilled with his new toy, but less than ecstatic when it clicked off mid-15-second elapsed times at the drag strip. Now, 325-horse/automatic Chevelles were not 13-second rides from the factory, but we figured a high-14 was within the realm of possibility. We wanted to see what this bad boy made to the rear tires.

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Equipped with a stock Quadrajet, and only enhanced with an Edelbrock 2.0 polished intake manifold and a set of Flowmaster mufflers, this Glacier Blue A-body was perfect for a chassis-dyno tuning session. We hauled our test mule down to Tune Time Performance in Toms River, New Jersey, where we strapped the Chevelle to the Mustang dyno in search of some free power

In addition to seeing what the car made near-stock trim and what we could squeeze out of it, we also decided to pit the Quadrajet (enter your favorite detracting name here) against a pair of Holley carbs we had lying around. We brought with us a Holley 750 HP double-pumper and a Holley 670 cfm Street Avenger vacuum secondary mixer.

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Not only would we tune up our Qaudrajet-equipped 396/325 powerplant, but we would also try and make some more power with a couple of carburetors. Thankfully, Holley shipped out a 670 cfm Street Avenger carb for us to play with.

We started out by baselining the Chevelle, but had to abort the first pull because the air/fuel reading showed that the engine was way too lean (16.1). After adjusting the mixture screws on the the Quadrajet, the 396 pumped out 199 (corrected) horsepower and 274 lb-ft of torque.

With found the base timing coming in at 42 degrees overall, so this was the first tweak. We added 8 degrees, bringing the timing total to 50. We let the car rip again, and found six horsepower, bringing the total to 205, but more importantly the torque figure checked in at 284 lb-ft, a solid 10 lb-ft improvement.

With the Quadrajet pushing out as much as it could, we swapped to the big boy of the bunch, the 750 HP. After modifying the fuel lines as needed, we let the big-block sing once again, and even though the engine was now, as overheard by onlookers, "pig rich", the Chevelle eked out 206 horsepower and 291 lb-ft of torque. With the air/fuel well into the 11.5:1 range, we swapped the jets both front and back in search of a leaner reading and hopefully more horsepower. While the air/fuel settled in at 12.5:1, the power remained the same. While we gained one horsepower and seven lb-ft of torque, the 750 HP would certainly have proven to be more favorable if the Rat was inhaling through something like an Edelbrock Performer RPM and exhaling through a set of headers instead of factory manifolds.

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After a drag test of this Glacier Blue '69 Chevelle SS396, we decided a trip to the chassis dyno to eek some more power out of this bad boy was needed. The results may surprise you.

Not only would we tune up our Qaudrajet-equipped 396/325 powerplant, but we would also try and make some more power with a couple of carburetors. Thankfully, Holley shipped out a 670 cfm Street Avenger carb for us to play with.

Before a dyno pull was made, contributor Dan Foley checked the timing of the Rat, and he popped the cap off the old-school dual-point distributor to see how much mechanical advance was available. Base timing was at 42 degrees, and thanks to the soft spring in the distributor, all of it was in at 1,500 rpm.

After an aborted first dyno pull that forced us to adjust the Quadrajet, the Rat thumped out 199 horsepower and 274 lb-ft of torque. Knowing that the car was lazy through the rpm range, we added 8 degrees of timing, bringing it up to 50 total. The result was the big-block waking up from its slumber, and the Quadrajet-equipped powerplant cracking off 205 horsepower and 284 lb-ft of torque. Just by adding timing and making sure the Quadrajet was tuned, we gained six horsepower and 10 lb-ft of torque without replacing a part.

Satisfied we weren't going to make much more power with the Quadrajet, we swapped over to the Holley 750 HP. The 750 upped output to 206 horses and 291 lb-ft of torque, but the air/fuel ratio showed the car was running extremely rich. It wasn't something we could fix by playing with the mixture screws, so we had to crack the bowls open and change jets.

The 750 was square all around with 73 jets, but we needed to lean it out a bundle. We dropped the primary jets down to 71s, and the secondaries to 68s. That's a two-step and a five-step downgrade front and back. The result was a better air/fuel ratio, but the same power.

Last but not least, we laid down the 670 cfm Street Avenger carb atop the 396. Even though the air/fuel gauge showed a slightly lean condition, it didn't warrant us to lift our foot off the throttle, and the Chevelle cranked out 195 horsepower and 281 lb-ft of torque. We tried playing with the mixture screws to lower the air/fuel, but to no avail. Alas, we were going to have to change jets.

Not wanting to mess with the great tip-in the 670 gave us, we only adjusted the primary side of the fuel mixer. The primary jets were 65s, while the secondaries were 68s, showing that the primary circuit was a bit leaner. With that in mind, we went up four jet sizes to 69s, and then slammed the loud pedal down one last time. The result was 199 horsepower and 287 lb-ft of torque.